Ceramic molded body comprising a photocatalytic coating and method for production the same

ABSTRACT

The invention relates to a ceramic moulded body consisting of an oxide ceramic base material and comprising a surface which self-cleans by means of water-sprinkling or percolation. Said moulded body has a porous, oxide ceramic coating which is photocatalytically active and has a specific surface of between approximately 25 m 2 /g and approximately 200 m 2 /g, preferably between approximately 40 m 2 /g and approximately 150 m 2 /g. The invention also relates to a method for producing one such ceramic moulded body.

The invention concerns a ceramic molded body of oxide-ceramic basematerial with a surface which is self-cleaning upon spraying orsprinkling with water and a process for the production thereof.

EP 0 590 477 B1 discloses a building material which can be for examplean outside wall material or roof material, wherein a thin metal oxidefilm with a photocatalytic action is applied on the surface of thebuilding material. The metal oxide film is preferably applied by meansof sol-gel processes. A titanium dioxide thin film building material ispreferably produced using titanium dioxide sol. The thin metal oxidefilm known from EP 0 590 477 B1 has deodorosing anti-mold properties.

By virtue of its film-like structure the metal oxide film known from EP0 590 477 B1 is of a small surface area and accordingly has a low levelof catalytic activity.

DE 199 11 738 A1 discloses a titanium dioxide photocatalyst which isdoped with Fe³⁺ ions and which has a content of pentavalent ions, whichis equimolar or approximately equimolar in relation to the Fe³⁺ ions.The titanium dioxide photocatalyst known from DE 199 11 738 A1 and dopedwith Fe³⁺ ions is produced by way of sol-gel processes.

EP 0 909 747 A1 discloses a process for producing a self-cleaningproperty of surfaces, in particular the surface of roof tiles, uponbeing sprayed or sprinkled with water. The surface has hydrophobicraised portions of a height of between 5 and 200 μm in distributed form.To produce those raised portions, a surface is wetted with a dispersionof powder particles of inert material in a siloxane solution and thesiloxane is then hardened. The process known from EP 0 909 747 A1 makesit possible to produce a ceramic body having a surface to whichparticles of dirt can cling poorly. The ceramic body known from EP 0 909747 A1 does not have any catalytic activity whatsoever.

WO 01/79141 A1 discloses a further process for producing a self-cleaningproperty of a surface and an article produced with that process. Inaccordance with that process, a metallorganic compound of titanium oxideis applied to a surface by means of a sol-gel process, the surface isdried and then subjected to heat treatment at elevated temperature. Thesurface of the titanium oxide layer can be subsequently hydrophobised.

The object of the present invention is to provide a molded body, inparticular roof materials, which has an improved self-cleaningcapability and improved stability such as for example improvedresistance to abrasion.

A further object of the invention is to provide a process for theproduction of such an improved ceramic molded body.

The object of the invention is attained by a ceramic molded body ofoxide-ceramic base material with a surface which is self-cleaning uponspraying or sprinkling with water, wherein the molded body has a porousoxide-ceramic coating, wherein the coating is photocatalytically activeand has a specific surface area in a range of between about 25 mg²/g andabout 200 m²/g, preferably between about 40 m²/g and about 150 m²/g.

Preferred developments of the ceramic molded body are set forth inappendant claims 2 through 18.

The object of the invention is further attained by a process for theproduction of a ceramic molded body of oxide-ceramic base material witha surface which is self-cleaning upon spraying or sprinkling with water,wherein the molded body has a photocatalytically active, porous,oxide-ceramic coating with a specific surface area in a range of betweenabout 25 m²/g and about 200 m²/g, preferably about 40 m²/g and about 150m²/g, wherein the process includes the following steps:

(a) mixing photocatalytically active, oxide-ceramic powder, adjustingagent and/or adhesive and a liquid phase to afford a suspension,

(b) applying the suspension produced in step a) to the oxide-ceramicbase material to produce a layer, and

(c) hardening the layer afforded in step (b) to produce aphotocatalytically active, porous, oxide-ceramic coating.

Preferred developments of that process are recited in appendant claims20 through 43.

The ceramic molded body produced using the process according to theinvention involves a highly suitable porosity and stability.

Unlike the sol-gel processes preferably used in the state of the art forthe production of coatings, in accordance with the invention asuspension of photocatalytically active, oxide-ceramic powder withfurther components is applied to an oxide-ceramic base material. Thistherefore does not involve producing a film but a porous structure oflarge specific surface area.

The structure produced is a highly porous structure, that is to say thespecific surface area of the catalytically active, porous, oxide-ceramiccoating is in a range of between 25 m²/g and 200 m²/g, furtherpreferably in a range of between about 40 m²/g and about 150 m²/g. Morepreferably the specific surface area is in a range of between 40 m²/gand about 100 m²/g.

With a specific surface area of about 50 m²/g a highly satisfactorycatalytic activity in respect of the applied oxide-ceramic coating isachieved. In that respect the mean layer thickness of the oxide-ceramiccoating is preferably in a range of between about 50 nm and about 50 μm,further preferably between about 100 nm and about 10 μm. A highlysatisfactory catalytic activity is obtained with a layer thickness ofabout 1 μm.

The photocatalytically active, porous, oxide-ceramic coating accordingto the invention provides that mold, fungal and plant growth, forexample moss, algae etc, bacterial contamination etc, which aredeposited on or in the ceramic molded body are photochemically brokendown and removed. The photocatalytic activity of the porous,oxide-ceramic coating is extremely advantageously adequate at ambienttemperature to oxidise and thus break down the stated substances andcontamination. The oxidised substances have a reduced adhesioncapability and are easily flushed off the surface of the molded bodyaccording to the invention when subjected to the action of spraying orsprinkling with water.

It is assumed that the photocatalytically active coating can have anoxidative action on the one hand directly on the organic contaminationand impurities. On the other hand it is assumed that the oxidativeeffect of the photocatalytically active coating is effected indirectlyby the production of oxygen radicals which subsequently oxidise andaccordingly break down the contaminating substances or impurities.

The self-cleaning action of the ceramic molded body according to theinvention can be further enhanced if a surface structure with raisedportions or depressions is arranged under the photocatalytically active,porous, oxide-ceramic coating and/or if the photocatalytically active,porous, oxide-ceramic coating itself has a surface structure with raisedportions and recesses.

It has been found that ceramic surface structures with raised portions,preferably involving a predetermined distribution density, have asurprising self-cleaning property. The raised portions can also behydrophobised so that the adhesion of hydrophilic soiling substances orcontaminants is further greatly reduced.

The raised portions can be formed by the application of particulatematerial to the ceramic base material. In that respect preferablytemperature-resistant crushed material is used as the particulatematerial, preferably selected from the group which consists of crushedstone, fire clay, clay, minerals, ceramic powder such as SiC, glass,glass chamotte, and mixtures thereof.

It will be appreciated that TiO₂, Al₂O₃, SiO₂, and/or Ce₂O₃ can be usedas the particulate material. In that respect particles of a size in arange of up to 1500 nm, preferably between about 50 nm and about 700 nm,have proven to be highly suitable. In addition a particle size range ofbetween about 50 nm and about 200 nm is highly preferred.

It is preferred that the raised portions or recesses are of heights ordepths respectively in a range of up to 1500 nm, preferably betweenabout 50 nm and about 700 nm, further preferably between about 50 nm andabout 200 nm. In that way the raised portions can also be formed withthe aggregation or agglomeration of smaller particles.

In that respect the particulate material can be fixed to the ceramicbase material using adhesives. For example the adhesives used can bepolysiloxanes which on the one hand fix the particulate material to thesurface of the oxide-ceramic base material and on the other hand providethe produced coating with a superhydrophobic surface. The adhesive, forexample the polysiloxane, is added in step (a) of the process accordingto the invention in production of the suspension.

If hydrophobisation of the surface of the coating is to be maintained,in that case the hardening operation in step (c) is not to be effectedat a temperature of more than 300° C. If the temperature is increasedabove 300° C., that can involve thermal decomposition of thepolysiloxane and the breakdown of the superhydrophobic surface on thephotocatalytically active, porous, oxide-ceramic coating.

It will be appreciated that other adhesives, preferably of organicnature, such as for example carboxymethylcelluloses, can also be used.

When calcining the ceramic molded body which is usually effected in arange of between more than 300° C. and about 1100° C., the particulatematerial used for producing raised portions is subjected to the actionof a temperature which results in superficial softening of the particlesurfaces so that a sinter-like join is produced between the particulatematerial and the oxide-ceramic base material. In that respect it is forexample also possible to add fluxing agents which reduce the sinteringtemperature.

The man skilled in the art is aware from EP 0 909 747, EP 00 115 701 andEP 1 095 023 of various possible ways of fixing particulate material ona ceramic surface. The contents of EP 0 909 747, EP 00 115 701 and EP 1095 923 are hereby incorporated by reference thereto.

Preferably, the photocatalytically active, porous, oxide-ceramic coatingis formed by using photocatalytically active, oxide-ceramic materialsselected from the group consisting of TiO₂, Al₂O₃, SiO₂, Ce₂O₃ andmixtures thereof.

In accordance with a further preferred embodiment the above-mentionedphotocatalytically active, oxide-ceramic materials may also be containedin the oxide-ceramic base body.

In accordance with a preferred embodiment the photocatalytically active,oxide-ceramic material in the coating and/or in the oxide-ceramic basematerial includes TiO₂ or Al₂O₃, optionally in combination with furtheroxide-ceramic materials. For example mixtures of titanium dioxide andsilicon dioxide, titanium dioxide and aluminum dioxide, aluminum dioxideand silicon dioxide and also titanium dioxide, aluminum oxide andsilicon dioxide have been found to be highly suitable.

In that respect preferably titanium dioxide with an anatase structure isused as the titanium dioxide. The aluminum oxide used is preferablyaluminum oxide C which is to be allocated crystallographically to theδ-group and has a strong oxidation-catalytic effect.

A suitable aluminum oxide C can be obtained from Degussa AG, Germany.For example AEROSIL COK 84, a mixture of 84% AEROSIL 200 and 16%aluminum oxide C has proven to be very usable in the present invention.

When using TiO₂ in the oxide-ceramic coating it is preferable that theTiO₂ is present at least in part in the anatase structure, preferably inrespect of at least 40% by weight, preferably in respect of at least 70%by weight, further preferably in respect of at least 80% by weight, withrespect to the total amount of TiO₂.

TiO₂ which is present in a mixture of about 70-85% by weight anatase andabout 30-15% by weight rutile has proven to be highly suitable.

Preferably the TiO₂ used in the present invention is obtained by flamehydrolysis of TiCl₄ in the form of highly disperse TiO₂ which preferablyhas a particle size of between about 15 nm and 30 nm, preferably 21 nm.

By way of example, it is possible to use for that purpose the titaniumdioxide which can be obtained under the name titanium dioxide P25 fromDegussa AG, Germany and which comprises a proportion of 70% anatase formand 30% rutile. Extremely advantageously titanium dioxide in the anataseform absorbs UV light at wavelengths of less than 385 nm. Rutile absorbsUV light at a wavelength of less than 415 nm.

In accordance with a preferred development the ceramic molded bodyaccording to the invention has a superhydrophobic surface.

It has been found that the self-cleaning property of the surface can bemarkedly improved if the photocatalytically active, porous,oxide-ceramic coating is provided with a superhydrophobic surface. Theoxidised organic soiling substances are still more easily flushed awayfrom the surface by spraying or sprinkling with water.

In accordance with the invention the term superhydrophobic surface isused to denote a surface with an edge angle of at least 140° for water.The edge angle can be determined in conventional manner at a drop ofwater of a volume of 15 μl, which is put on to a surface.

Preferably the edge angle is at least 150°, further preferably 160°,still further preferably at least 170°.

The photocatalytically active, porous, oxide-ceramic coating can behydrophobised using Ormoceres, polysiloxane, alkylsilane and/orfluorosilane.

Preferably a mixture of SiO₂ and fluorosilane is applied, therebyproducing a superhydrophobic surface. That hydrophobising effect or theprovision of a superhydrophobic surface is extremely advantageous forthe self-cleaning property of the molded body according to theinvention.

In accordance with a further preferred embodiment the superhydrophobicsurface has raised portions. Those raised portions can be produced whenapplying the hydrophobising agent by a procedure whereby particulatematerial is added to the hydrophobising agent and that mixture issubsequently applied to the photocatalytically active, porous,oxide-ceramic coating.

When the surface is hydrophobised with the above-specifiedhydrophobising agents, the temperature may not be raised above 300° C.as that can then involve thermal decomposition, which has already beenmentioned above, of the hydrophobising agents.

Therefore in accordance with the invention hardening is effected bycalcining only when no hydrophobic surface has yet been applied to thephotocatalytically active, porous, oxide-ceramic coating. Ifpolysiloxane were used as an adhesive and subsequently the molded bodywere hardened by calcining, the surface usually has to be hydrophobisedonce again if a hydrophobic surface is to be afforded on thephotocatalytically active, porous, oxide-ceramic coating.

Preferably the ceramic molded body is in the form of a roof tile, atile, a clinker brick or a facade wall.

In the production according to the invention of a ceramic molded bodythe photocatalytically active, oxide-ceramic powder used in step (a) ispreferably in a nano-disperse form. In that respect the particle sizerange of the oxide-ceramic powder in a range of between 5 nm and about100 nm, further preferably between about 10 nm and about 50 nm, hasproven to be highly suitable.

To produce the ceramic molded body according to the invention apreferably homogenous suspension is produced from oxide-ceramic powder,adjusting agent and/or adhesive and a liquid phase, by mixing. Thatsuspension can be applied in a desired layer thickness to theoxide-ceramic base material.

The suspension may be applied to the oxide-ceramic base material forexample by pouring, brushing, spraying, flinging and so forth. It willbe appreciated that the oxide-ceramic base material can also be dippedinto the suspension.

Preferably the suspension is applied in such a layer thickness that,after the drying and/or calcining operation, the result obtained is aceramic molded body with a photocatalytically active, porous,oxide-ceramic coating in a thickness of between 50 nm and about 50 μm,preferably between about 100 nm and about 10 μm.

The layer thickness of the undried suspension is usually in a range ofbetween about 0.5 μm and about 100 μm.

The oxide-ceramic base material may be a green body (uncalcined ceramicmaterial) or a pre-calcined or calcined ceramic material.

Preferably organic viscosity regulators, for examplecarboxymethylcellulose, are used as the adjusting agent. Those viscosityregulators impart a suitable viscosity to the suspension so that it canbe reliably applied to the ceramic base material in the desired layerthickness. Extremely advantageously, the organic adjusting agent,preferably the carboxymethylcellulose, burns when the operation ofhardening the layer is effected by calcining in a temperature range ofbetween more than 300° C. and about 1100° C. Due to burning of theorganic adjusting agent, the formation of a porous structure in thephotocatalytically active, porous, oxide-ceramic coating is favored. Inthat situation the organic adjusting agent preferably burns completelyand preferably without residue, forming a porous structure.

Calcination of the layer produced in step (b) can be effected on the onehand by calcining the molded body in a calcining furnace or in acalcining chamber at a temperature of more than 300° C. to about 1100°C. In addition the calcining operation is preferably effected in atemperature range of between about 700° C. and about 1100° C.

The drying operation is effected at a substantially lower temperaturethan the calcining operation. Drying is usually effected in atemperature range of between 50° C. and 300° C., preferably between 80°C. and 100° C. In that temperature range an applied superhydrophobiccoating is not broken down or destroyed.

When using adhesive there is preferably added to the suspensionpolysiloxane which promotes adhesion of the oxide-ceramic powder to theoxide-ceramic base material. Besides its adhesive effect polysiloxanealso results in hydrophobisation of the structure. In addition additionof adhesive such as for example polysiloxane also produces an increasein the viscosity of the suspension produced in step (a) of the processaccording to the invention. Accordingly an adjusting agent does notnecessarily have to be added when adding adhesive to the suspension instep (a). The viscosity which is adjusted using adhesive can besufficient so that in step (b) the suspension can be applied to theoxide-ceramic base material, to form a layer.

The liquid phase used is preferably water.

In a further configuration of the process particulate material can alsobe added to the suspension produced in step (a). In this alternativeconfiguration of the process, the raised portions which are advantageousin regard to the self-cleaning effect of the surface and also thecatalytically active, porous, oxide-ceramic coating are produced in onestep.

In a ceramic molded body produced in accordance with this alternativeconfiguration of the process, there is then not a separate layerstructure consisting of a layer with raised portions and, arrangedthereover, catalytically active, porous, oxide-ceramic coating. Rather,the raised portions produced using particulate material and thephotocatalytically active, oxide-ceramic components are present insubstantially mutually juxtaposed relationship or intimately mixed witheach other.

Optionally a hydrophobising agent can then also be added to thatsuspension so that superhydrophobisation of the oxide-ceramic surface iseffected in the same step in the process. In this alternative form ofthe process the hardening operation can then be effected only by dryingso that no thermal decomposition of the superhydrophobic surface occurs.

It will be appreciated that it is also possible firstly for theabove-mentioned particulate material to be applied to the oxide-ceramicbase material to produce raised portions and for it to be fixed to thesurface of the ceramic base material by means of adhesive and/orsintering, for that surface which is prepared in that way and which hasraised portions to be provided with a photocatalytically active, porous,oxide-ceramic coating using the process according to the invention, andfor a superhydrophobic surface optionally to be subsequently produced onthe photocatalytically active coating.

The hydrophobising agents used are preferably inorganic-organic hybridmolecules such as for example siloxanes, in particular polysiloxanes. Inaddition Ormoceres, alkylsilanes and/or fluorosilanes have proven to besuitable as the hydrophobising agents.

The hydrophobising agents can be applied by a suitable process, forexample spraying, pouring, flinging, sprinkling etc. For example,firstly a hydrophobising solution or suspension can be produced using apreferably aqueous liquid phase. Optionally particulate materials canalso be added to that hydrophobising solution or suspension if raisedportions are to be produced in the superhydrophobic surface. Thathydrophobising solution or suspension can then be applied in theabove-described conventional manner.

The term superhydrophobic surface is used in accordance with theinvention to denote a superhydrophobic layer, wherein the edge angle forwater is at least 140°, preferably 160°, further preferably 170°.

In addition, a pre-drying step can also be carried out after applicationof the suspension produced in step (a) to the oxide-ceramic basematerial, prior to the calcining operation. In that pre-drying step theliquid phase, preferably water, can be removed by evaporation. That canbe effected for example by heating, for example in a circulating airfurnace or a radiant furnace. It will be appreciated that it is alsopossible to use other drying processes, for example using microwavetechnology.

The pre-drying step has proven to be advantageous in order to avoidcracking or tearing of the layer produced from the suspension, in thecalcining operation.

After the calcining operation a superhydrophobic surface can then beapplied in the above-described manner.

In a preferred embodiment, after the calcining step and the optionallyimplemented hydrophobising operation, it is possible to carry out apost-treatment of the photocatalytically active, porous, oxide-ceramiccoating produced. The post-treatment is effected by irradiation withlaser light, or NIR or UV light. That post-treatment can improve theadhesion between the photocatalytically active coating and theoxide-ceramic base material.

It has been found that the ceramic molded body according to theinvention, besides an improved self-cleaning property, also has improvedmechanical stability. There is the very great advantage that thecatalytically active, porous, oxide-ceramic coating with a possiblysuperhydrophobic surface adheres very firmly and reliably to the ceramicbase material. Thus when that coating is applied for example to rooftiles it is not destroyed or abraded when a person walks on the roof.

1. A ceramic molded body, more specifically a roof tile, tile, clinkerbrick or facade wall, of oxide-ceramic base material with a surfacewhich is self-cleaning upon spraying or sprinkling with water,characterized in that the molded body has a porous oxide-ceramiccoating, wherein the coating is photocatalytically active and containsTiO₂ and has a specific surface area in a range of between 25 mg²/g, and200 m²/g, preferably between 40 m²/g and 150 m²/g, wherein the TiO₂ isproduced by flame hydrolysis of TiCl₄ as highly disperse TiO₂.
 2. Aceramic molded body as set forth in claim 1 characterized in that thecoating has a specific surface area in a range of between 40 m²/g and100 m²/g.
 3. A ceramic molded body as set forth in claim 1,characterized in that the mean layer thickness of the coating is in arange of between 50 nm and about 50 μm, preferably 100 nm and 10 μm. 4.A ceramic molded body as set forth in claim 1, characterized in thatarranged between the oxide-ceramic base material and thephotocatalytically active, porous, oxide-ceramic coating is at least onelayer with raised portions, the oxide-ceramic base material has raisedportions and/or the photocatalytically active, porous, oxide-ceramiccoating is in the form of a layer with raised portions.
 5. A ceramicmolded body as set forth in claim 4 characterized in that the raisedportions are formed by particulate material fixed to the oxide-ceramicbase material.
 6. A ceramic molded body as set forth in claim 5characterized in that the particulate material is temperature-resistantground material preferably selected from the group which consists ofground rock, fire clay, clay, minerals, ceramic powder such as SiC,glass, glass chamotte and mixtures thereof.
 7. A ceramic molded body asset forth in claim 5 or claim 6 characterized in that the size of theparticles and/or the raised portions is or are in a range of up to 1500nm, preferably of between 50 nm and 700 nm, further preferably between50 nm and 200 nm.
 8. A ceramic molded body as set forth in claim 1,characterized in that the photocatalytically active, porous,oxide-ceramic coating includes additionally photocatalytically active,oxide-ceramic materials selected from the group which consists of Al₂O₃,SiO₂ and mixtures thereof.
 9. A ceramic molded body as set forth inclaim 1, characterized in that the oxide-ceramic base material of themolded body includes photocatalytically active, oxide-ceramic materialsselected from the group which consists of TiO₂, Al₂O₃, SiO₂ and mixturesthereof.
 10. A ceramic molded body as set forth in claim 1,characterized in that the photocatalytically active, oxide-ceramicmaterial has an average particle size in the range of between 5 nm and100 nm, preferably between 10 nm and 50 nm.
 11. A ceramic molded body asset forth in claim 1, characterized in that the TiO₂ contained in thephotocatalytically active, porous, oxide-ceramic coating and/or in theoxide-ceramic base material is present at least in part and preferablyin respect of at least 40% by weight with respect to the total amount ofTiO₂, in the anatase structure.
 12. A ceramic molded body as set forthin claim 1, characterized in that the TiO₂ contained in thephotocatalytically active, porous, oxide-ceramic coating and/or in theoxide-ceramic base material is present in respect of at least 70% byweight with respect to the total amount of TiO₂, in the anatasestructure.
 13. A ceramic molded body as set forth in claim 1,characterized in that the TiO₂ is present in a mixture comprising 70% byweight of anatase and 30% by weight of rutile.
 14. A ceramic molded bodyas set forth in claim 1, characterized in that the coating has asuperhydrophobic surface, wherein the superhydrophobic surface has acontact or edge angle of at least 140° for water.
 15. A ceramic moldedbody as set forth in claim 14 characterized in that the superhydrophobicsurface of the coating is produced using Ormoceres, polysiloxane,alkylsilane and/or fluorosilane, preferably in combination with SiO₂.16. A ceramic molded body as set forth in one of claims 14 and 15characterized in that the superhydrophobic surface of the coating hasraised portions.
 17. A ceramic molded body as set forth in claim 16characterized in that the raised portions of the superhydrophobicsurface are produced using particulate material.
 18. A process for theproduction of a ceramic molded body, more specifically a roof tile,tile, clinker brick or facade wall, of oxide-ceramic base material witha surface which is self-cleaning upon spraying or sprinkling with water,wherein the molded body has a photocatalytically active, porous,oxide-ceramic TiO₂-containing coating with a specific surface area in arange of between 25 m²/g and 200 m²/g, preferably 40 m²/g and 150 m²/g,wherein the process includes the following steps: (a) mixingphotocatalytically active, oxide-ceramic powder which contains TiO₂,wherein the TiO₂ is produced by flame hydrolysis of TiCl₄ as highlydisperse TiO₂, adjusting agent and/or adhesive and a liquid phase toafford a suspension, (b) applying the suspension produced in step (a) tothe oxide-ceramic base material to produce a layer, and (c) hardeningthe layer afforded in step (b) to produce a photocatalytically active,porous, oxide-ceramic coating.
 19. A process as set forth in claim 18characterized in that at least one layer with raised portions is appliedto the oxide-ceramic base material in a preceding step and thesuspension produced in step (a) is applied to the oxide-ceramic basematerial provided with a layer with raised portions and subsequentlyhardened in step (c).
 20. A process as set forth in claim 19characterized in that particulate material is additionally added in step(a).
 21. A process as set forth in claim 18 or claim 19 characterized inthat the raised portions are formed by fixing particulate material onthe oxide-ceramic base material.
 22. A process as set forth in claim 20characterized in that the particulate material is temperature-resistantground material preferably selected from the group which consists ofground rock, fire clay, clay, minerals, ceramic powder such as SiC,glass, glass chamotte and mixtures thereof.
 23. A process as set forthin claim 20, characterized in that the mean particle size of theparticulate material is in a range of up to 1500 nm, preferably between50 nm and 700 nm, further preferably between 50 nm and 200 nm.
 24. Aprocess as set forth in claim 18, characterized in that adjusting agentused in step (a) is an organic viscosity regulator.
 25. A process as setforth in claim 24 characterized in that carboxymethylcellulose is usedas the organic viscosity regulator.
 26. A process as set forth in claim18, characterized in that adhesive used in step (a) is polysiloxane. 27.A process as set forth in claim 18, characterized in that water is usedas the liquid phase in step (a).
 28. A process as set forth in claim 18,characterized in that the adhesion between the catalytically activecoating and the oxide-ceramic base material is improved by a procedurewhereby the photocatalytically active, porous, oxide-ceramic coatingproduced in step (c) is irradiated with laser light or NIR or UV light.29. A process as set forth in claim 18, characterized in that thephotocatalytically active, oxide-ceramic powder used in step (a)additionally includes materials selected from the group which consistsof Al₂O₃, SiO₂ and mixtures thereof.
 30. A process as set forth in claim18, characterized in that contained in the oxide-ceramic base materialof the molded body are photocatalytically active, oxide-ceramicmaterials selected from the group which consists of TiO₂, Al₂O₃, SiO₂and mixtures thereof.
 31. A process as set forth in claim 18,characterized in that the photocatalytically active, oxide-ceramicpowder used in step (a) includes particles in the range of between 5 nmand 100 nm, preferably between 10 nm and 50 nm.
 32. A process as setforth in claim 18, characterized in that the TiO₂ contained in thephotocatalytically active, oxide-ceramic powder and/or in theoxide-ceramic base material is present at least in part and preferablyin respect of at least 40% by weight with respect to the total amount ofTiO₂ in the anatase structure.
 33. A process as set forth in claim 18,characterized in that the TiO₂ contained in the photocatalyticallyactive, oxide-ceramic powder and/or in the oxide-ceramic base materialis present in respect of at least 70% by weight with respect to thetotal amount of TiO₂ in the anatase structure.
 34. A process as setforth in claim 18, characterized in that the TiO₂ contained in thephotocatalytically active, oxide-ceramic powder and/or in theoxide-ceramic base material is present in a mixture comprising 70% byweight of anatase and 30% by weight of rutile.
 35. A process as setforth in claim 18, characterized in that the layer produced in step (b)is hardened in step (c) by drying at a temperature of up to 300° C.and/or by calcining at a temperature of more than 300° C. to 1100° C.36. A process as set forth in claim 35 characterized in that the layerproduced in step (b) is at least partially pre-dried prior to thecalcining operation in step (c) by evaporation of the liquid phase. 37.A process as set forth in claim 18, characterized in that the coatinghardened in step (c) is hydrophobised to provide a superhydrophobicsurface, wherein the superhydrophobic surface has a contact or edgeangle of at least 140° for water.
 38. A process as set forth in claim18, characterized in that a hydrophobising agent is additionally addedin step (a) and the coating produced in step (b) is hardened in step (c)by drying at a temperature of up to 300° C.
 39. A process as set forthin claim 37 or claim 38 characterized in that an inorganic-organichybrid molecule, preferably a polysiloxane solution is used forhydrophobisation.
 40. A process as set forth in claim 37 or claim 38characterized in that Ormoceres, alkylsilane and/or fluorosilane,preferably in a mixture with SiO₂, is used for the hydrophobisationoperation.
 41. A process as set forth in claim 37 or 38, characterizedin that particulate material is added to produce a superhydrophobicsurface with raised portions in the hydrophobisation operation.
 42. Useof highly disperse TiO₂ produced by flame hydrolysis of TiO₄ in anoxide-ceramic coating for roof tile, tile, clinker brick or a facadewall.